PIL5, a phytochrome-interacting bHLH protein, regulates gibberellin responsiveness by binding directly to the GAI and RGA promoters in Arabidopsis seeds

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Previous work showed that PHYTOCHROME-INTERACTING FACTOR3-LIKE5 (PIL5), a light-labile basic helix-loop-helix protein, inhibits seed germination by repressing GIBBERELLIN 3b- HYDROXYLASE1 (GA3ox1) and GA3ox2 and activating a gibberellic acid (GA) catabolic gene (GA2ox2). However, we show persistent light-dependent and PIL5-inhibited germination behavior in the absence of both de novo GA biosynthesis and deactivation by GA2ox2, suggesting that PIL5 regulates not only GA metabolism but also GA responsiveness. PIL5 increases the expression of two GA repressor (DELLA) genes, GA-INSENSITIVE (GAI) and REPRESSOR OF GA1-3 (RGA/RGA1), in darkness. The hypersensitivity of gai-t6 rga-28 to red light and the suppression of germination defects of a rga-28 PIL5 overexpression line show the significant role of this transcriptional regulation in seed germination. PIL5 also increases abscisic acid (ABA) levels by activating ABA biosynthetic genes and repressing an ABA catabolic gene. PIL5 binds directly to GAI and RGA promoters but not to GA and ABA metabolic gene promoters. Together, our results show that light signals perceived by phytochromes cause a reduction in the PIL5 protein level, which in turn regulates the transcription of two DELLA genes directly and that of GA and ABA metabolic genes indirectly.
Publisher
AMER SOC PLANT BIOLOGISTS
Issue Date
2007-04
Language
English
Article Type
Article
Keywords

ABSCISIC-ACID; FLORAL DEVELOPMENT; SIGNALING PATHWAYS; FLOWERING TIME; LIGHT CONTROL; RED-LIGHT; GERMINATION; THALIANA; GENE; DEGRADATION

Citation

PLANT CELL, v.19, no.4, pp.1192 - 1208

ISSN
1040-4651
DOI
10.1105/tpc.107.050153
URI
http://hdl.handle.net/10203/90424
Appears in Collection
CH-Journal Papers(저널논문)BS-Journal Papers(저널논문)
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